Abrasive Blade Tips With Additive Resistant to Clogging By Organic Matrix Abradable

ABSTRACT

An abrasive tip comprises an additive, the additive is configured to prevent adhesion of an organic component from an abradable seal onto an abrasive blade tip.

BACKGROUND

This disclosure relates to abrasive tips for rotatable blades. Abradableseals or coatings (rub coatings) can be used to protect moving partsfrom damage during rub interaction while providing a small clearance.Such seals are used in turbomachines to interface with abrasive tips ofa rotating blade stage.

The abrasive tips include coatings to enhance performance and limit heatgeneration and heat transfer to the blade. The abrasive tips, uponrubbing the abradable seal, remove portions of the abradable seal. Theportions of the abradable seal can transfer to the abrasive tips andadhere to the abrasive tips. Carbonized portions of the abradable sealthat adhere to the abrasive tips can build up. The portions of thecarbon based materials that build up between the grit particles of theabrasive tip (i.e. clogging) can cause frictional heating during rubevents. The frictional heating can affect the polyurethane erosionresistant coating on the gas path surfaces of the blade. Thus, the veryproblem that the abrasive blade tip is designed to prevent, insteadoccurs through a different mechanism. Pending U.S. non-provisionalapplication no. US 2015/0233255 is incorporated herein by reference.

What is needed is an abrasive tip that resists clogging due to build-upof carbonized rub debris.

SUMMARY

In accordance with the present disclosure, there is provided an abrasiveblade tip comprising an additive configured to prevent adhesion of anorganic component of an abradable seal onto the abrasive blade tip.

In another and alternative embodiment, the additive is selected from thegroup consisting of solid lubricant, zinc stearate, calcium stearate,hexagonal boron nitride, magnesium stearate, lithium fluoride andmolydisulfide.

In another and alternative embodiment, the abrasive blade tip comprisesa metal matrix, the additive and hard particles dispersed through themetal matrix.

In another and alternative embodiment, the additive is configured toprevent clogging of the spaces between the hard particles that protrudefrom the abrasive blade tip.

In another and alternative embodiment, the additive is configured toincorporate into rub debris comprising constituents of the organicmatrix composite.

In another and alternative embodiment, the additive is configured tolubricate the organic component responsive to a rub event with theabrasive blade tip.

In accordance with the present disclosure, there is provided a gasturbine engine comprises a compressor section; a combustor fluidlycoupled to the compressor section; a turbine section fluidly coupled tothe combustor; a fan rotatably coupled with the turbine section, the fanincluding a plurality of circumferentially-spaced rotary blades, each ofthe blades comprising an airfoil section extending between leading andtrailing edges, first and second opposed sides each joining the leadingand trailing edges and an inner end opposite a free tip end; the airfoilincluding a polymeric overcoat on at least one of the leading edge,trailing edge, first side and second side, and each airfoil sectionincluding an abrasive tip at the free tip end, said abrasive tipcomprising an additive, and a seal circumscribing the plurality ofcircumferentially spaced rotatable blades, the seal comprising anorganic matrix composite comprising an organic component, the additiveconfigured to prevent adhesion of the organic component onto theabrasive tip, the seal configured contactable with, and abradable by,the abrasive tip.

In another and alternative embodiment, the respective compositions ofthe seal and the abrasive tip being complimentarily selected withrespect to frictional heat generated and heat-induced delamination ofthe polymeric overcoat.

In another and alternative embodiment, the additive is selected from thegroup consisting of solid lubricant, zinc stearate, calcium stearate,hexagonal boron nitride, magnesium stearate, lithium fluoride andmolydisulfide.

In another and alternative embodiment, the abrasive tip comprises ametal matrix, additive and hard particles dispersed through the metalmatrix; wherein the additive is configured to prevent clogging of thespaces between the hard particles that protrude from the abrasive bladetip.

In another and alternative embodiment, the additive is configured tolubricate the organic component responsive to a rub event with theabrasive blade tip.

In another and alternative embodiment, the additive is configured toincorporate into rub debris comprising constituents of the organicmatrix composite.

In accordance with the present disclosure, there is provided a rotorsystem, such as a fan, comprising a plurality ofcircumferentially-spaced rotary blades, each of the blades comprising anairfoil section extending between leading and trailing edges, first andsecond opposed sides each joining the leading and trailing edges and aninner end opposite a free tip end; the airfoil including a polymericovercoat on at least one of the leading edge, trailing edge, first sideand second side, and each airfoil section including an abrasive tip atthe free tip end, the abrasive tip comprising an additive, and a sealcircumscribing the plurality of circumferentially spaced rotatableblades, the seal comprising an organic matrix composite with an organiccomponent, the additive configured to prevent adhesion of the organiccomponent onto the abrasive tip, the seal configured contactable with,and abradable by, the abrasive tip.

In another and alternative embodiment, the additive is selected from thegroup consisting of solid lubricant, zinc stearate, calcium stearate,hexagonal boron nitride, magnesium stearate, lithium fluoride andmolydisulfide.

In another and alternative embodiment, the abrasive tip comprises ametal matrix, additive and hard particles dispersed through the metalmatrix; wherein the additive is configured to prevent clogging of thespaces between the hard particles that protrude from the abrasive bladetip.

In another and alternative embodiment, the additive is configured tolubricate the organic component responsive to a rub event with theabrasive blade tip.

In another and alternative embodiment, the additive is configured toincorporate into rub debris comprising constituents of the organicmatrix composite.

Other details of the abrasive blade tip are set forth in the followingdetailed description and the accompanying drawing wherein like referencenumerals depict like elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example gas turbine engine.

FIG. 2 illustrates an isolated view of the fan section of the gasturbine engine of FIG. 1.

FIG. 3 illustrates an abrasive tip interfacing with an abradable seal.

FIG. 4 illustrates a cross-section of an abrasive tip.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmenter section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flow path B in abypass duct defined within a fan case 15, and into a core flow path C tothe compressor section 24 for compression and communication into thecombustor section 26 then expansion through the turbine section 28.Although depicted as a two-spool turbofan gas turbine engine in thedisclosed non-limiting embodiment, it should be understood that theconcepts described herein are not limited to use with two-spoolturbofans as the teachings may be applied to other types of turbineengines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis A relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a first (or low) pressure compressor 44 and afirst (or low) pressure turbine 46. The inner shaft 40 is connected tothe fan 42 through a speed change mechanism, which in exemplary gasturbine engine 20 is illustrated as a geared architecture 48 to drivethe fan 42 at a lower speed than the low speed spool 30. The high speedspool 32 includes an outer shaft 50 that interconnects a second (orhigh) pressure compressor 52 and a second (or high) pressure turbine 54.A combustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 is arranged generally betweenthe high pressure turbine 54 and the low pressure turbine 46. Themid-turbine frame 57 further supports bearing systems 38 in the turbinesection 28. The inner shaft 40 and the outer shaft 50 are concentric androtate via bearing systems 38 about the engine central longitudinal axisA which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of combustor section 26 or even aft ofturbine section 28, and fan section 22 may be positioned forward or aftof the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five (5:1). Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present invention isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption” (TSFC)—is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that operating point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tram ° R)/(518.7°R)]^(0.5). The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150ft/second.

FIG. 2 illustrates an isolated view of the fan section 22 of the engine20. The fan 42 includes a rotor 60 that has a plurality ofcircumferentially-spaced blades 62. Each blade 62 includes an airfoilsection 64 that extends between leading and trailing edges 66/68, firstand second opposed sides 70/72 that each joins the leading and trailingedges 66/68, and an inner end 74 and a free tip end 76. Each bladeincludes an abrasive tip 78 at the free tip end 76.

The fan case 15 is annular in shape and circumscribes the blades 62. Thefan section 22 is designed such that the abrasive tips 78 of the blades62 rub against the fan case 15 during rotation. In this regard, the fancase 15 includes an abradable seal 80 mounted on a radially inner sideof the fan case 15.

When two components are in rubbing contact, at least one of thecomponents may wear. The term “abradable” refers to the one of the twocomponents that wears, while the other component is “abrasive” and doesnot wear or wears less. Thus, when the abrasive tips 78 of the blades 62rub against the seal 80, the seal 80 will be worn whereas the abrasivetips 78 will not wear or will wear less than the seal 80. The word“abrasive” thus also implies that there is or can be contact with anabradable component.

FIG. 3 shows a cutaway view of a representative portion of the airfoilsection 64 of one of the blades 62 and a portion of the abradable seal80. The airfoil section 64 is formed of a metal-based material with apolymeric overcoat 62 a on the surfaces thereof. For example, thepolymeric overcoat 62 a serves to protect the underlying airfoil section64 from erosion due to foreign particulate ingested into the engine 20.In one example, the metal-based material of the airfoil section 64 is analuminum alloy.

The polymeric coating 62 a can be a polyurethane-based coating, anepoxy-based coating, or a silicone rubber-based coating, but is notlimited to these types of polymeric coatings or materials. The polymericcoating 62 a can cover the first and second sides 70/72 of the blades 62and can span the entire lateral surface of the blade 62 between theleading and trailing edges 66/68.

Friction between a blade tip and a surrounding case generates heat. Theheat can be conducted into the case, into the blade, or both. However,in particular for metal blades and polymeric-based cases, the metal ofthe blade is generally a better thermal conductor than the polymer ofthe case, and a majority of the heat thus can conduct into the blade.While this may normally not present any detriments for a plain metalblade, the heat conduction can be detrimental to a metal blade that hasa polymeric overcoat because the heat can cause delamination of thepolymeric overcoat and thus compromise the erosion protection. In thisregard, the abrasive tip 78 has a composition selected with respect toheat-induced delamination of the polymeric overcoat 62 a from frictionalheat generated during rubbing between the abrasive tip 78 and theabradable seal 80. That is, the respective compositions of the abradableseal 80 and the abrasive tip 78 are complimentarily selected withrespect to frictional heat generated and heat-induced delamination ofthe polymeric overcoat 62 a. For example, the compositions are selectedwith regard to a blade temperature at which the polymeric overcoat 62 adoes not delaminate nor has defined delamination durability over anextended period of time, such as the life of the engine 20.

The abradable seal 80 is formed of a polymeric-based material, such as apolymer matrix composite. In one further example, the polymer matrixcomposite includes an epoxy matrix and a silica-containing fillerdispersed through the matrix. In a further example, thesilica-containing filler is or includes hollow glass microspheres. Anexample is 3M™ Scotch-Weld™ Structural Void Filling Compound EC-3555.

FIG. 4 illustrates a cross-section of representative portion of afurther example of the abrasive tip 78. In this example, the abrasivetip 78 includes a metal matrix 90, hard particles 92, and an additive 94dispersed through the metal matrix 90. In one further example, the metalmatrix 90 and the metal-based material of the airfoil section 64 arecompositionally composed of the same predominant metal, which canpromote strong adhesion if the abrasive tip 78 interfaces with themetal-based material (i.e., the abrasive tip 78 is in direct contactwith the metal-based material, as depicted in FIG. 4). As an example,the metal can be aluminum.

-   -   Incorporated into the abrasive tip 78 is the additive, release        agent or solid lubricant or simply additive 94. The additive 94        is blended into the matrix composite of the abrasive tip 78. The        additive 94 can comprise a metal stearate. In exemplary        embodiments, the additive 94 can comprise stearates or        palmitates of zinc, aluminum, barium, calcium, strontium and the        like. The additive 94 can comprise solid lubricants such as        hexagonal boron nitride, lithium fluoride and moly disulfide.        The additive 94 can be a suspension or solution of the calcium        stearate or other metal stearate, or solid lubricant with a        solid binder component. The additive 94 is compatible with        plastic materials and other solid binders such as PVA (poly        vinyl alcohol) and acrylic latex emulsion (Duramax B1001, Rohm        and Haas Co., Philadelphia, Pa.).

The thermally sprayed aluminum and abrasive composite coating of theabrasive tip 78 can be produced by plasma spraying of aluminum powder,abrasive powder and solid lubricant powder. The powders may be blended,fed separately or in the form of composite particles. After inclusion inthe coating, the solid lubricant will get smeared across the blade tipby the wear debris during rub interaction with the abradable seal 80.

An example tip treatment can be created by plasma spraying a compositeabrasive coating with the addition of about 2.5 wt % of crushed calciumstearate particles injected to the plasma stream through a separatepowder port. The calcium stearate having a nominal size of 75 microns.The resultant coating containing about 0.5 to 5 volume % of solidlubricant.

The additive 94 becomes incorporated into the rub debris upon a rubevent. The additive 94 within the rub debris prevents the organiccompounds of the abradable seal 80 from adhering to the abrasive bladetip 78. Since the components of the abradable seal 80 are prevented fromadhering to the abrasive tip 78, then clogging of the abrasive tip 78between the cutting surfaces can be prevented.

In one further example, the metal matrix 90 is a eutecticaluminum-silicon alloy having a composition, by atomic weight, of 88%aluminum and 12% silicon. The eutectic composition provides highhardness and strength to enhance holding the hard particles 92 in themetal matrix 90. The eutectic composition also has good high temperatureproperties and retains strength at high temperatures rather thansoftening.

In one further example, the metal matrix 90 is, or predominantlyincludes, aluminum, and the hard particles 92 are, or predominantlyinclude, alumina (Al₂O₃). In an additional example, the hard particles92 are, or predominantly include, zirconia (ZrO₂). In yet anotherexample, the hard particles 92 are, or predominantly include, aluminaand zirconia. It is to be understood that the hard particles 92 are notlimited to alumina and zirconia, and other oxides, nitrides, carbides,oxycarbides, oxynitrides, diamond and combinations thereof can be usedselectively, with respect to heat-induced delamination of the polymericovercoat 62 a from frictional heat generated during rubbing between theabrasive tip 78 and the abradable seal 80.

The abrasive tip 78 can have a thickness in a thickness range of0.025-1.3 millimeters, and the hard particles 92 can have an averagemaximum dimension in a particle size range of 10-200 micrometers. Thehard particles 92 may protrude from the metal matrix 90 or be completelycovered by the metal matrix.

In one further example a polymer matrix filled with hollow glassmicrospheres for the abradable seal 80 is complimentary with a metalmatrix 90 of aluminum and hard particles 92 of alumina, zirconia, orboth in the abrasive tip 78, with respect to frictional heat generatedand heat-induced delamination of the polymeric overcoat 62 a. That is,the frictional heat generated between the abradable seal 80 and theabrasive tip 78 cause a blade 62 temperature at which the examplepolymer of the polymeric overcoat 62 a does not delaminate, or at leastmeets delamination durability over an extended period of time, such asthe life of the engine 20.

In the illustrated example in FIG. 4, the hard particles 92 are facetedand thus have angled facets 92 a. The angled facets 92 a providerelatively sharp corners that facilitate efficient “cutting” through theabradable seal 80 with low cutting forces, which lowers frictions and,in turn, contributes to lowering the amount of heat generated. In oneexample, the hard particles 92 are DURALUM ATZ II that has approximately40% tetragonal zirconia with titania evenly distributed throughout theindividual alumina grains.

The additive 94 helps to prevent clogging of the spaces between the hardparticles 92 that protrude, as the hard particles are exposed to theupper surface of the metal matrix 90.

The benefit of the additive 94 in the abrasive tip 78 is to preventthermal damage to the polyurethane erosion resistant coating 62 a on theblades. This is accomplished by preserving the cutting ability of theabrasive tips 78. By incorporating the additive into the abrasive tip,the entire operation of applying surface treatments to the blade tipabrasive can be eliminated and present a cost effective alternative.

The present composite abrasive coating with “anti-clogging” constituentwill expand the range of rub conditions under which effective abrasivecutting will take place and thereby significantly reduce the possibilityof thermal damage to the erosion resistant coating at the blade tips.

Although a combination of features is shown in the illustrated examples,not all of them need to be combined to realize the benefits of variousembodiments of this disclosure. In other words, a system designedaccording to an embodiment of this disclosure will not necessarilyinclude all of the features shown in any one of the Figures or all ofthe portions schematically shown in the Figures. Moreover, selectedfeatures of one example embodiment may be combined with selectedfeatures of other example embodiments.

There has been provided an organic matrix abradable seal resistant toclogging of abrasive blade tips. While the abrasive blade tip has beendescribed in the context of specific embodiments thereof, otherunforeseen alternatives, modifications, and variations may becomeapparent to those skilled in the art having read the foregoingdescription. Accordingly, it is intended to embrace those alternatives,modifications, and variations which fall within the broad scope of theappended claims.

What is claimed is:
 1. An abrasive blade tip comprising: an additiveconfigured to prevent adhesion of an organic component of an abradableseal onto the abrasive blade tip.
 2. The abrasive blade tip according toclaim 1, wherein said additive is selected from the group consisting ofsolid lubricant, zinc stearate, calcium stearate, hexagonal boronnitride, magnesium stearate, lithium fluoride and molydisulfide.
 3. Theabrasive blade tip according to claim 1, wherein said abrasive blade tipcomprises a metal matrix, said additive and hard particles dispersedthrough said metal matrix.
 4. The abrasive blade tip according to claim3, wherein said additive is configured to prevent clogging of the spacesbetween the hard particles that protrude from the abrasive blade tip. 5.The abrasive blade tip according to claim 1, wherein said additive isconfigured to incorporate into rub debris comprising constituents of anorganic matrix composite of said abradable seal.
 6. The abrasive bladetip according to claim 1, wherein said additive is configured tolubricate said organic component responsive to a rub event with saidabrasive blade tip.
 7. The abrasive blade tip according to claim 1,wherein said additive is dispersed throughout said abrasive blade tip.8. A gas turbine engine comprising: a compressor section; a combustorfluidly coupled to said compressor section; a turbine section fluidlycoupled to said combustor; a fan rotatably coupled with said turbinesection, said fan including a plurality of circumferentially-spacedrotary blades, each of said blades comprising an airfoil sectionextending between leading and trailing edges, first and second opposedsides each joining the leading and trailing edges and an inner endopposite a free tip end; said airfoil including a polymeric overcoat onat least one of the leading edge, trailing edge, first side and secondside, and each airfoil section including an abrasive tip at said freetip end, said abrasive tip comprising an additive; and a sealcircumscribing the plurality of circumferentially spaced rotatableblades, said seal comprising an organic matrix composite and an organiccomponent, said additive configured to prevent adhesion of said organiccomponent onto said abrasive tip, said seal configured contactable with,and abradable by, said abrasive tip.
 9. The turbine engine componentaccording to claim 8, wherein the respective compositions of said sealand said abrasive tip being complimentarily selected with respect tofrictional heat generated and heat-induced delamination of saidpolymeric overcoat.
 10. The turbine engine component according to claim8, wherein said additive is selected from the group consisting of solidlubricant, zinc stearate, calcium stearate, hexagonal boron nitride,magnesium stearate, lithium fluoride and molydisulfide.
 11. The turbineengine component according to claim 8, wherein said abrasive tipcomprises a metal matrix, said additive and hard particles dispersedthrough said metal matrix; wherein said additive is configured toprevent clogging of the spaces between the hard particles that protrudefrom the abrasive blade tip.
 12. The turbine engine system according toclaim 8, wherein said additive is configured to lubricate said organiccomponent responsive to a rub event with said abrasive blade tip. 13.The turbine engine system according to claim 8, wherein said additive isconfigured to incorporate into rub debris comprising constituents ofsaid organic matrix composite.
 14. A rotor system comprising: aplurality of circumferentially-spaced rotary blades, each of said bladescomprising an airfoil section extending between leading and trailingedges, first and second opposed sides each joining the leading andtrailing edges and an inner end opposite a free tip end; said airfoilincluding a polymeric overcoat on at least one of the leading edge,trailing edge, first side and second side, and each airfoil sectionincluding an abrasive tip at said free tip end, said abrasive tipincluding an additive, and a seal circumscribing the plurality ofcircumferentially spaced rotatable blades, said seal comprising anorganic matrix composite comprising an organic component, said additiveconfigured to prevent adhesion of said organic component onto saidabrasive tip, said seal configured contactable with, and abradable by,said abrasive tip.
 15. The rotor system claim 14, wherein said additiveis selected from the group consisting of solid lubricant, zinc stearate,calcium stearate, hexagonal boron nitride, magnesium stearate, lithiumfluoride and molydisulfide.
 16. The rotor system claim 14, wherein saidabrasive tip comprises a metal matrix and hard particles dispersedthrough said metal matrix; wherein said additive is configured toprevent clogging of the spaces between the hard particles that protrudefrom the abrasive blade tip.
 17. The rotor system claim 14, wherein saidadditive is configured to lubricate said organic component responsive toa rub event with said abrasive blade tip.
 18. The rotor system claim 14,wherein said additive is configured to incorporate into rub debriscomprising constituents of said organic matrix composite.